DESCRIPTION

New applications should use the POSIX.1-specified "utmpx" versions of
these functions; see CONFORMING TO.

utmpname()
sets the name of the utmp-format file for the other utmp
functions to access.
If
utmpname()
is not used to set the filename
before the other functions are used, they assume _PATH_UTMP, as
defined in <paths.h>.

setutent()
rewinds the file pointer to the beginning of the utmp file.
It is generally a good idea to call it before any of the other
functions.

endutent()
closes the utmp file.
It should be called when the user
code is done accessing the file with the other functions.

getutent()
reads a line from the current file position in the utmp file.
It returns a pointer to a structure containing the fields of
the line.
The definition of this structure is shown in
utmp(5).

getutid()
searches forward from the current file position in the utmp
file based upon ut.
If ut->ut_type is one of RUN_LVL,
BOOT_TIME, NEW_TIME, or OLD_TIME,
getutid()
will
find the first entry whose ut_type field matches ut->ut_type.
If ut->ut_type is one of INIT_PROCESS, LOGIN_PROCESS,
USER_PROCESS, or DEAD_PROCESS,
getutid()
will find the
first entry whose
ut_id
field matches ut->ut_id.

getutline()
searches forward from the current file position in the utmp file.
It scans entries whose
ut_type
is USER_PROCESS
or LOGIN_PROCESS and returns the first one whose
ut_line
field
matches ut->ut_line.

pututline()
writes the
utmp
structure ut into the utmp file.
It uses
getutid()
to search for the proper place in the file to insert
the new entry.
If it cannot find an appropriate slot for ut,
pututline()
will append the new entry to the end of the file.

RETURN VALUE

getutent(),
getutid(),
and
getutline()
return a pointer to a struct utmp on success,
and NULL on failure (which includes the "record not found" case).
This struct utmp is allocated in static storage, and may be
overwritten by subsequent calls.

On success
pututline()
returns
ut;
on failure, it returns NULL.

utmpname()
returns 0 if the new name was successfully stored, or -1 on failure.

ERRORS

ENOMEM

Out of memory.

ESRCH

Record not found.

setutent(),
pututent(),
and the
getut* ()
functions can also fail for the reasons described in
open(2).

FILES

/var/run/utmpdatabase of currently logged-in users

/var/log/wtmpdatabase of past user logins

CONFORMING TO

XPG2, SVr4.

In XPG2 and SVID 2 the function
pututline()
is documented to return void, and that is what it does on many systems
(AIX, HP-UX, Linux libc5).
HP-UX introduces a new function
_pututline()
with the prototype given above for
pututline()
(also found in Linux libc5).

All these functions are obsolete now on non-Linux systems.
POSIX.1-2001, following SUSv1,
does not have any of these functions, but instead uses

These functions are provided by glibc,
and perform the same task as their equivalents without the "x", but use
struct utmpx,
defined on Linux to be the same as
struct utmp.
For completeness, glibc also provides
utmpxname(),
although this function is not specified by POSIX.1.

On some other systems,
the utmpx structure is a superset of the utmp structure,
with additional fields, and larger versions of the existing fields,
and parallel files are maintained, often
/var/*/utmpx
and
/var/*/wtmpx.

Linux glibc on the other hand does not use a parallel utmpx file
since its utmp structure is already large enough.
The functions getutxent()
etc. are aliases for getutent() etc.

NOTES

Glibc Notes

The above functions are not thread-safe.
Glibc adds reentrant versions

These functions are GNU extensions, analogs of the functions of the
same name without the _r suffix.
The
ubuf
argument gives these functions a place to store their result.
On success they return 0, and a pointer to the result is written in
*ubufp.
On error these functions return -1.
There are no utmpx equivalents of the above functions.
(POSIX.1 does not specify such functions.)

EXAMPLE

The following example adds and removes a utmp record, assuming it is run
from within a pseudo terminal.
For usage in a real application, you
should check the return values of
getpwuid(3)
and
ttyname(3).